Carbon Dioxide Was Gas Fatal To 1,200

August 26, 1986|By Ronald Kotulak, Science writer.

The deadly cloud that reportedly killed at least 1,200 people near a crater lake in northern Cameroon is the worst natural disaster caused by volcanic gases in recorded history, according to volcanologists.

``This is totally unprecedented for a volcanic gas kill,`` said Terrence Gerlach, chief of geochemistry at Sandia National Laboratory, Albuquerque, N.M.

``It behooves us to learn how this kind of natural disaster occurred because there are a lot of crater lakes in Africa with the potential for causing many more deaths,`` he said.

While information coming from the Cameroon tragedy is still sparse, geologists believe that enormous amounts of gas trapped at the bottom of Lake Nios were suddenly released and smothered nearby village residents.

Although people reportedly smelled hydrogen sulfide, which has the odor of rotten eggs, the killer gas probably was carbon dioxide, said Alfred Anderson Jr., a University of Chicago geophysicist.

Denser than air, carbon dioxide would lie close to the ground, asphyxiating people by depriving them of oxygen, he said.

``At night, when there is little air circulation, the gas would sit in low-lying areas and basically suffocate anyone who happened to be there,``

said Anderson. ``They really wouldn`t know what happened to them.

``This is a well-known hazard, and it is the reason that we never pitch tents in low lying areas around volcanoes,`` he said.

A similar incident occurred in the same area in 1984, when 37 people reportedly died. A team of University of Rhode Island geologists headed by Haraldur Sigurdsson went to Cameroon after that episode and found extremely high concentrations of carbon dioxide in the water and lake bottom sediment.

The scientists concluded that a landslide churned up part of the lake bottom, releasing large amounts of carbon dioxide, and that it was the carbon dioxide that asphyxiated the 37 natives and killed much wildlife.

Observers at that time described a whitish, smoke-like cloud that drifted off the lake and sank into valleys and other low-lying areas. What caused the cloud to appear whitish is not known; but the fact that it was close to the ground indicates a high concentration of carbon dioxide, according to scientists.

Gerlach said the three main gases released by volcanic activity are water vapor, carbon dioxide and sulfur dioxide. In addition, there are small amounts of many other gases, including hydrogen sulfide, hydrogen chloride, hydrogen fluoride and carbon monoxide.

Like other crater lakes, Lake Nios fills the mouth of an old volcano. Dormant for many years, the crater becomes filled with sediment and finally fills with water.

As hot lava far below the lake rises through vents toward the surface, it releases enormous amounts of gas, said Gerlach. The gases rise to the lake bottom, where they become trapped in the sediment and clay like a giant bubble, he explained.

Natives reported hearing an explosion during the night that preceded the release of the deadly cloud.